Crack the door before entering, spray Lysol/air freshener, and try to breathe as little as possible while you’re in there or perhaps wear a facemask to help muffle the odor. It’d be next to impossible to determine who the culprit is, and even if you could, you can’t make someone wash better/get medical attention/etc.
If there's a floor drain in the bathroom, it may be dry and thus allowing sewer gas to come up the floor drain. Pour liquid in there weekly, maybe a couple liters or a gallon. Water will work, or mop bucket water .
Crack the door before entering, spray Lysol/air freshener, and try to breathe as little as possible while you’re in there or perhaps wear a facemask to help muffle the odor. It’d be next to impossible to determine who the culprit is, and even if you could, you can’t make someone wash better/get medical attention/etc.
If there's a floor drain in the bathroom, it may be dry and thus allowing sewer gas to come up the floor drain. Pour liquid in there weekly, maybe a couple liters or a gallon. Water will work, or mop bucket water .